PC unexpectedly turns off (not shut down).

Short Summary: My desktop unexpectedly turns off (note, does not shut down, but simply turns off), usually while I am playing high intensity games, like Playerunknown Battlegrounds. To circumvent this problem, I bought and installed a new power supply (750W). The issue happens less frequently, but has still happened twice since installing the new power supply a couple weeks ago. There are no beeps sounding when I boot, and there are no error messages or warnings given.

Specs:
See attached DxDiag.txt.

I appreciate any suggestions for how to combat this. Please let me know what I can do to assist in this process. Thanks.

Remember this is your typical AMD system that hits repair counters all over. After the PSU the motherboard is suspect. You usually find this after a few years of hard use. The owners want proof and if you have the board you offer the fix for a price. If they don't you return it with a note about the motherboard plus the CPU and maybe RAM. No reason to estimate less than this.

To your initial response: My computer's no longer under warranty. I think I void the warranty by installing a new PSU and an additional HDD, both of which I've done. I'd have to look further into th at. I realize it may be the motherboard, in which case that really sucks, but I was hoping to bring it here to see if there was anything that stuck out to anyone.

Any chance of a web speccy report? It tells me a lot about age, temps, what's running, bios version, HDD health and so on.

Without that I have to go with the most common parts we replace. You already did the PSU and why that helps is the new PSU gives bettery quality power (less ripple, etc.) So the motherboard and its aged electrolytic capacitors don't have to work as hard. But under load still may lock up. If it just powers down, it could be heat. Try it with the cover off and a fan pointing at the machine. If that helps then it's time for the million mile work over. Deep clean heatsinks, replace all heatsink compound and replace slow or failed fans.

AMD FX-8320: 79 °C
That's toasty for what looks like a light load. Nod to the million mile service (clean all heatsinks and replace all heatsink compound on all heatsinks. I mean it. ALL.) Check fans, replace slow and failed ones.

If you didn't replace the power supply, then you'd still be under warranty? I'd still call tech support about it, if it still would have been under warranty. I fried my motherboard by adding the wrong kind of memory on my first computer. It was Dell, but I called tech support and they sent me a replacement motherboard for free. Worst thing they can say is no.

Make sure the fans on your GPU are working, make sure the fan on you CPU is working and your heatsink is not full of fluff. Always good to change the paste on your CPU every couple of years. Make sure your PSU has enough power to support your GPU.
If you have a fault try and talk to seller if you can come to some arrangement for a service.
I always service my PC and clean it out. 79 degrees is rather hot for a CPU.